Selecting part of a field with a regex

Question

I\'ve a table where a 3rd party component stores urls, i would like to get only the id parameter from this url.

With PHP i can do it like this:

Answer 1

No, sad to say MySQL doesn't have a way to apply a regex to a column's contents in a SELECT clause, only a WHERE clause.

But you can use ordinary (non-regex) string manipulation functions to do this. If the column containing your ampersand-separated parameter string is named url, you can get the id number with this fine string expression, which finds your id number.

  CAST(RIGHT(url, LENGTH(url) - 3 - LOCATE('&id=', url)) AS SIGNED INTEGER)

So, if you want a list of id values from the url columns of table1, you could use this SELECT query.

SELECT CAST(RIGHT(url, LENGTH(url) - 3 - 
                       LOCATE('&id=', url)) AS SIGNED INTEGER) AS id
  FROM table1
 WHERE url REGEXP '&id=[0-9]+'

As you can see this uses the regexp search function to locate the appropriate rows.

There is nothing fast about this. Regexp matching can't exploit a MySQL index. If you have the choice of loading your table with the id column pre-extracted you'll be much better off searching when your table gets big.